Overall, I thought it was cool. I can picture a kind of dark sorcerer/magician figure conjuring up a spell or something.
There are parts of it that sound pretty dark and "evil," but there are others (where it transitions into a major key, for instance) where it doesn't really convey the "dark" feeling you seem to be going for. While the contrast is good, a more sinister sound might make more sense.
Also, from around 1:50 to 2:00 it sounded a bit odd (the harmonies don't seem to have much direction, and the melody is rather disjointed in a similar manner), although it might just be the MIDI playback causing that.
Really not bad. Have you written for strings before?